The invention relates to a light receiving device for an optical encoder, and an optical encoder. In particular, the invention relates to a light receiving device for an optical encoder using photodiodes and an optical encoder equipped with the same.
An optical encoder comprises a light emitting unit and a light receiving unit that are oppositely arranged. The optical encoder is configured so that it can detect signal changes when a scale appropriately provided with a transparent pattern and a light shielding pattern is passed between the light emitting unit and the light receiving unit. The optical encoder can be used as a position detecting means with a required resolution by appropriately setting pitches of the light receiving unit and the scale (e.g., Japanese Laid-Open Patent Application 2002-340669). Optical encoders are used for various applications such as detecting the position of a print head in a printer and controlling the amount of paper feed in a copier.
However, in conventional optical encoders, the size of the photodiode in the light receiving unit must be very small for enhancing the spatial resolution, which causes a problem that they are not easy to manufacture.
In addition, in conventional optical encoders, the photocurrent waveform obtained from the light receiving device has a high DC component, which causes a problem that the dynamic range is narrowed.
The present invention provides a light receiving device for an optical encoder, and an optical encoder, being easy to enhance spatial resolution and also capable of reducing the DC component in photocurrent.